1. Field of the Invention
This invention relates to high voltage, solid state inverters used in such applications as motor drives and custom power applications. More particularly, it relates to such inverters in which cascaded multiple voltage level inverter modules provide a high voltage output with a reduced number of transformers and rectifiers needed to provided isolated dc power to the modules.
2. Background Information
High voltage inverters such as those used in motor drives or in custom power applications frequently require a step-up transformer to boost a relatively low inverter voltage up to the application voltage. To eliminate this step-up transformer, it is known to use series-connected switching devices to generate the desired high voltage directly. This method suffers from difficulties in maintaining equal sharing of voltage across the device string and relatively high harmonics. Another technique for eliminating the need for a step-up transformer is to connect inverter H bridges in series. This results in better control of the device voltages and lower output harmonics. However, each inverter bridge requires a separate energy supply transformer winding or other energy source.
There is a need therefore for an improved high voltage inverter that avoids the problem of voltage sharing associated with inverters relying on series-connected switches to generate the desired high voltage.
There is an associated need for such a high voltage inverter with reduced harmonics.
There is a further need for such an inverter which can produce high voltages with a reduced number of isolated dc energy sources required.
There is a particular need for such high voltage inverters using transformers and a rectification stage to produce the dc voltage required which minimize the number of secondary transformer windings required.